Seite - 23 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

1.6 Plotting,PrintingandInputData 23 Thecharacteristicsofaplotted linemayalsobechangedinmanywayswith just minor modifications of the plot command. For example, a black line is achieved with plt.plot(t, y, ’k’) # k - black, b - blue, r - red, g - green, ... Other colors could be achieved by exchanging thekwith certain other letters. For example, using b, you get a blue line, r gives a red line, while gmakes the line green. In addition, the line style may be changed, either alone, or together with a colorchange.Forexample, plt.plot(t, y, ’--’) # default color, dashed line plt.plot(t, y, ’r--’) # red and dashed line plt.plot(t, y, ’g:’) # green and dotted line Note that toavoiddestroyingapreviouslygeneratedplot,youmayprecedeyour plotcommandby plt.figure() Thiscausesa newfigure to becreatedalongsideanyalreadypresent. Plotting Points Only When there are not too many data points, it is sometimes desirable to plot each data point as a “point”, rather than representing all the data points with a line. To illustrate, we may consider our case with the ball again, but this time computing the height each 0.1s, rather than every millisecond. In ball_plot.py,we would thenhave to changeourcall tolinspace into t = np.linspace(0, 1, 11) # 11 values give 10 intervals of 0.1 Note that we need to give 11 as the final argument here, since there will be 10 intervals of 0.1s when 11 equally distributed values on [0,1] are asked for. In addition, we would have to change the plot command to specify the plotting of data points as “points”. To mark the points themselves, we may use one of many differentalternatives,e.g.,acircle (the lowercase lettero)orastar (*).Usingastar, forexample, theplotcommandcould read plt.plot(t, y, ’*’) # default color, points marked with * With thesechanges, the plot fromFig.1.1wouldchangeas seen inFig.1.2. Ofcourse,notonlycanwechoosebetweendifferentkindsofpointmarkers,but also their colormaybespecified.Someexamplesare: plt.plot(t, y, ’r*’) # points marked with * in red plt.plot(t, y, ’bo’) # points marked with o in blue plt.plot(t, y, ’g+’) # points marked with + in green When are the data points “too many” for plotting data points as points (and not as a line)? If plotting the data pointswith point markersand those markersoverlap in the plot, the pointswill not appear as points, but rather as a very thick line. This ishardlywhatyouwant.